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The subjects of the program, nine chimpanzees, were reared in a laboratory environment which was specifically meant to stimulate their intellect by being complex and stimulating, as animals raised otherwise fail to thrive (for example, their appetites might otherwise decline). This was in contrast to the traditional psychology lab where the animals are caged and remain in solitude. The animals are:

The language designed by Premack for an ape was not verbal; Premack's chimpanzee program differed from that of a separate research program in which other chimpanzees, were raised in a human family in parallel with human babies, and taught words3. Eventually, the chimpanzees might get to a two-year-old human's list of words, but no further. Vicki (chimpanzee) was eventually trained to speak four words3. The experiments on those chimpanzees did not demonstrate the existence of the faculties shown by Sarah (chimpanzee) discussed below, in her command of a language, for example. In other experiments, other chimpanzees have been taught American Sign Language, notably Washoe (chimpanzee)11.12 Washoe could use 68 gestures after three years of training, eventually getting to 150 gestures. However, Nim (chimpanzee)13, trained in American Sign Language, was found to demonstrate no forms with grammar, his linguistic productions being sets of gestures in no particular order. Koko (gorilla)14 and Chantek (orangutan)15 were also trained in American Sign Language. See also Kanzi's 200-word vocabulary of spontaneous productions as of 2005.

The language consisted of a series of coloredplastictokens, which the chimpanzees could manipulate and stick to a magneticboard. Each token stood for a word which was never spoken in the chimpanzee's presence. Sarah began her language training in 1967 at age 5, beginning with food exchanges, in order to establish a social exchange with the instructor. The Premacks note that the chimpanzees gave food reluctantly and unwillingly, far preferring to receive food. In a series of experiments, Premack was able to train Sarah, Elizabeth, and Peony to parse sentences:

which might result in Peony touching the trainer's nose.
The tokens did not resemble the objects; an apple was symbolized by a blue triangle token. The chimpanzee Elizabeth would be symbolized by a decorated E token, a copy of which would dangle from a necklace around her neck. The trainer would also wear a corresponding token, as would other investigators whom the chimpanzee would have to name in the formation of the targetsentence. It took Sarah, Elizabeth, and Peony each hundreds of trials to first form an association between the tokens and the objects. Sarah in particular was trained in the token manipulations for eighteen months.
Sarah was able to learn imperative sentences with a grammar,

Sarah jam bread take

in which the trainer allowed her to take the bread and jam, and also negative sentences

No Sarah honey cracker take

in which the trainer restrained her from taking the cracker and honey, which taught Sarah to suppress her impulse to take the negated object. In particular, the noun had to be at the beginning and the verb had to be at the end of the production, or else the trainer would not respond to Sarah's ungrammatical sentence. After hundreds of trials, Sarah could reliably produce the grammatical form

Sarah was also able to answer questions in the form of a question token "?" which she could answer by selecting a resolving token. However Sarah was never able to ask questions by manipulating the "?" token. The question "What is the color of apple?"

Premack was able to demonstrate that Sarah could understand how to decode a symbol stream after training. First she had to learn the token "name-of" and then learn that some new, but real objects had the name-of fig token1 and crackerjack token2.

She learned

Real fig name-of fig token1

and

Real crackerjack name-of crackerjack token2.

She was tested with

fig token1 "?" Real crackerjack

which she answered correctly with

fig token1 Not name-of Real crackerjack

Finally, with the trainer placing a ripe fig on the table, and the tokens fig token1, crackerjack token2, give, Mary, Sarah, orange, banana, Sarah produced the new sentence

Mary give fig token1 Sarah

and with the trainer placing a crackerjack on the table, Sarah produced the new sentence

Sarah, Peony, and Elizabeth were able to respond to and formulate analogies and to express judgements. In these trials, problems were formulated by videotapedsituations involving an actor, both friendly and unfriendly. With no training, and with observation of the laboratory only, Sarah was able to select answers requiring judgement, based on her experiences in the laboratory, such as the fact that a light cord had to be plugged in to solve some problems. Sarah was able to select proposed solutions for resolving the situations.

Sarah was most accurate on judgements of sameness, less so on similarity, and least accurate on judgements of difference. Human children were then tested with the same protocols, using speech. Young children passed the tests on number but failed on tests measuring conservation of liquid and solid. Five to six-year-old children passed the tests on conservation of liquid and solid, suggesting a similar process for the cognition of measurement of conservation of liquid and solid, between ape and human.

The chimpanzees do not spontaneously point outside of the psychological laboratory. The control chimpanzees, who were not trained in the language, could all point in order to communicate with the trainers.

Washoe (chimpanzee)11,12 was able to spontaneously sign, in contrast to Nim (chimpanzee)13. Kanzi (bonobo)17, at age 30 months demonstrated spontaneous production of gestures and keyboard presses to ask for desired objects or events, and to name items in response to queries from the trainer. Kanzi previously played in the training room where his adoptive mother Matata (bonobo) was being trained with gestures and keyboard presses ("Lexigrams") 16. The spontaneous productions by Kanzi occurred in the absence of Matata. Kanzi can currently produce 200 words and recognize 500.

The Premacks stated that the chimpanzees had specific traits, such as favorite trainers, and that some chimpanzees, such as Gussie seemed more fearful than the others. As previously noted, The Premacks noticed that Jessie seemed to be the brightest of the nine chimpanzee subjects. For example, she did not hesitate to unmask a masked researcher, which none of the other chimpanzees attempted. It is clear that the Premacks attempted to provide a humane, supportive environment for the chimpanzees.

Vauclair notes that chimpanzees will become distressed in the absence of their favorite companion. (Vauclair p. 76)